The Korean Supreme Court recently held that, even if an accused party’s mode of practice has a technical feature that is different from a patented invention, it may still be determined to be equivalent to the patented invention in a scope confirmation trial if a person of ordinary skill in the art could easily come up with such a different feature as of the time of adjudication (Supreme Court Case No. 2022 Hu 10210 dated February 2, 2023).

▶Background of the Case and Intellectual Property High Court (formerly Patent Court)¹ Decision 

The claimed invention of the subject patent related to novel compounds of general formula I, including dapagliflozin (), used as an oral agent for treating diabetes.

Petitioner, a generic competitor of the patentee, lodged a negative patent scope confirmation trial, seeking a declaratory judgement that the petitioner’s dapagliflozin formate (; an ester prodrug of dapagliflozin), did not fall within the scope of the patent claim.

The Trial Board ruled that the petitioner’s formate was not equivalent to the patented invention and, thus, fell outside the scope of the subject patent. Thereafter, the patentee filed an appeal before the Intellectual Property High Court.

The Intellectual Property High Court found that a person skilled in the art could easily change dapagliflozin to dapagliflozin formate, and it would be difficult to conclude that the patentee had intentionally excluded dapagliflozin formate from the scope of the subject invention during prosecution. Accordingly, the High Court determined that the petitioner’s formate was equivalent to the patented invention and fell within the scope of the patent claim.

▶Supreme Court Decision

On appeal, the Supreme Court held that the Intellectual Property High Court did not err in its decision on whether it would be obvious to change dapagliflozin to dapagliflozin formate and whether dapagliflozin formate was intentionally excluded.

The Supreme Court, however, noted that the Intellectual Property High Court decision was silent on the time for determining the equivalency. In this regard, the Supreme Court clarified that, considering the purpose of the doctrine of equivalents is to meaningfully protect a patent right by preventing attempts to avoid patent infringement through minor changes to an element of a patent claim, the Trial Board should have considered whether a person of ordinary skill in the art could easily come up with the change from dapagliflozin to dapagliflozin formate as of the time of the adjudication, even by referencing post-grant evidentiary materials such as references, which became available after the grant of the patent, showing that dapagliflozin was particularly effective as an oral agent for treating diabetes among the compounds of general formula I of the patented invention.

In so ruling, the Supreme Court noted that a person skilled in the art could easily change dapagliflozin to dapagliflozin formate as of the time of the decision of the scope confirmation trial in consideration of the following circumstances: (i) it was well known in the art to prepare a prodrug in an ester form by means of chemical modification of a hydroxy (-OH) group present in an active compound such as dapagliflozin; (ii) there was no technical difficulty in selecting an appropriate esterification site on dapagliflozin in order to synthesize dapagliflozin formate; and (iii) a formate was the simplest ester form that could be used and its good stability was known in the art.

Accordingly, the Supreme Court held that dapagliflozin formate was equivalent to the subject invention and affirmed the Intellectual Property High Court decision that dapagliflozin formate fell within the scope of the subject patent.

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¹ Please note that, as of February 16, 2023, the official English name of the “Patent Court” of Korea was changed to the “Intellectual Property High Court.”